Conventional systems for the mixing of fluids in different phases employ columns which may be packed columns, plate columns or bubble-cap columns, or columns with some other form of contact medium. In these systems, the various fluids generally flow countercurrently.
The prior art systems suffer the disadvantage that in order to achieve a significant degree of gas/liquid contact, the columns have to be large and their operation is hampered by excessive foaming. Also the turn-down ratio of countercurrent contactors is limited due to flooding. In addition, any subsequent stripping section which might be required to remove the gas from solution must also be large, to handle the large volume of solvent or reagent used. Since the operation may well be carried out under high pressure and since the fluids involved may be highly corrosive, the capital costs of the large columns and subsequent stripping section are high. Furthermore, operating costs and maintenance costs are high.
Conventional systems for the absorption of acid gases employ a liquid solvent; typical solvents include amines such as methyldiethanolamine (MDEA), monoethanolamine (MEA) and diethanolamine (DEA). Mixtures of solvents can also be used. These solvents may be contacted with the sour gas mixture (gas mixture including acid gases) in a column such as that described above. The same problems with the size of the column and the volume of solvent required as described above still apply.
Alternatively, the liquid reacting irreversibly (also called scavenger liquid), may be simply injected into the gas or passed through some form of nozzle (e.g. 0.2 mm wide) to try to break up or atomise the liquid and increase the surface area of liquid in contact with the gas. This liquid performs an irreversible reaction with the gas and is not stripped for subsequent re-use. This system suffers the disadvantage that the size of the nozzle required to atomise the liquid to an acceptable level is very small and easily blocked. It is also very difficult to atomise viscous liquids such as the scavenger solvents referred to above at decent turn-down ratios of the liquid flow rate (low liquid flow rates). A nozzle also only gives a point distribution of liquid which gives only localised mixing.
It is therefore an object of the present invention to overcome the problems referred to above and to provide a means for improved dispersed distribution of liquid into the gas over a wide range of liquid flow rates.
It is a further object of the present invention to provide a method of selectively absorbing a fluid component from a fluid mixture with a high degree of efficiency and more economically (lower chemical consumption to overcome the specification prescribed) than in existing methods. In particular, it is an object of the present invention to provide a method of selectively removing a selected gas component from a gas stream with a high degree of efficiency.